A serial interface such as the Universal Serial Bus (USB) is a technology which provides a fast, cabled data connection between a complex device (e.g. a PC) which is called the Host and a connected peripheral (e.g. a mouse, keyboard etc.) which is called the Device.
A serial interface according to the USB standard comprises two data lines (D+ and D−) a ground line (GND) and a voltage supply line (VBus).
According to the USB standard, the D+ and D− lines are configured to be used for data transfer.
The VBus line enables a connected device, which might not have an own power supply or where the device internal power supply is limited (e.g. a battery pack) to receive electrical power from the other connected device.
In accordance with the USB standard the devices roles (host role and device role) are fixed, i.e. by the type of connector of each device (A-plug and B-plugs) the role of the devices is defined and e.g. connection of one host to another host device is not possible.
The USB On-The-Go standard (USB OTG) extends the basic USB standard in such a way that the interface contains an additional identification (ID) line which enables the devices to switch and/or negotiate the host/device role of the connected devices.
According to the USB OTG standard the A-plug (connected to USB OTG host) the ID pin is connected to ground and the B-plug (connected to USB OTG device) the ID pin is left floating.
For a more detailed description of the USB OTG standard it is hereby referred to the USB OTG standard “On-The-Go Supplement to the USB 2.0 Specification; Apr. 4, 2006”.
Small devices like mobile phones, audio players, personal digital assistants and so on can only provide limited space for connectors and interfaces for connection to other devices and accessories.
For instance, traditionally audio devices that used 2.5 mm or 3.5 mm universal headsets (UHS) required a bulky and expensive 2.5 mm or 3.5 mm universal headset jack (UHJ). Devices that also provided USB functionality required two connectors.